In damascene processing, electrodeposition is commonly used to fill recessed features with cobalt or other metals to fabricate interconnects and other structures. In order to form high quality interconnects, it is important to establish void-free, seam-free fill. In traditional damascene processing, organic additives such as suppressor, accelerator, and leveler are used to establish a bottom-up fill mechanism where the feature is filled from the bottom upwards. The bottom-up fill mechanism forms much higher quality features compared to a conformal fill mechanism, which is likely to form voids and/or seams.
Where a conformal fill mechanism is used, the electrodeposited film is formed at a substantially uniform thickness at all regions of the recessed feature. As the film builds up on the sidewalls of the feature, the sidewalls close in toward one another, forming a seam up the middle of the feature. In many cases, as the sidewalls close in toward one another, they pinch off an area near the top of the feature, preventing electroplating from occurring effectively at positions lower in the feature. This effect leads to the formation of voids within the feature, which are highly undesirable. As mentioned above, these undesirable effects are traditionally avoided through the use of organic additives in the electrolyte that establish a bottom-up fill mechanism, explained further below.